Visible to Intel only — GUID: iga1401395384075
Ixiasoft
Visible to Intel only — GUID: iga1401395384075
Ixiasoft
9.2.1. MDIO Frame Format (Clause 45)
Field Name | Description |
---|---|
PRE | Preamble. 32 bits of logical 1 sent prior to every transaction. |
ST | The start of frame for indirect access cycles is indicated by the <00> pattern. This pattern assures a transition from the default one and identifies the frame as an indirect access. |
OP | The operation code field indicates the following transaction types: 00 indicates that the frame payload contains the address of the register to access. 01 indicates that the frame payload contains data to be written to the register whose address was provided in the previous address frame. 11 indicates that the frame is a read operation. The post-read-increment-address operation <10> is not supported in this frame. |
PRTAD | The port address (PRTAD) is 5 bits, allowing 32 unique port addresses. Transmission is MSB to LSB. A station management entity (STA)13 must have a prior knowledge of the appropriate port address for each port to which it is attached, whether connected to a single port or to multiple ports. |
DEVAD | The device address (DEVAD) is 5 bits, allowing 32 unique MDIO manageable devices (MMDs)14 per port. Transmission is MSB to LSB. |
TA | The turnaround time is a 2-bit time spacing between the device address field and the data field of a management frame to avoid contention during a read transaction. For a read transaction, both the STA and the MMD remain in a high-impedance state (Z) for the first bit time of the turnaround. The MMD drives a 0 during the second bit time of the turnaround of a read or postread-increment-address transaction. For a write or address transaction, the STA drives a 1 for the first bit time of the turnaround and a 0 for the second bit time of the turnaround. |
REGAD/ Data |
The register address (REGAD) or data field is 16 bits. For an address cycle, it contains the address of the register to be accessed on the next cycle. For the data cycle of a write frame, the field contains the data to be written to the register. For a read frame, the field contains the contents of the register. The first bit transmitted and received is bit 15. |
Idle | The idle condition on MDIO is a high-impedance state. All tri-state drivers are disabled and the MMDs pullup resistor pulls the MDIO line to a one. |